We begin with the shocking trial of the cleveland mother who has been charged with murdering her fiance, by poisoning his iced tea with antifreeze. She poisoned his drinks over weeks. Reporter: She's the mother of two, accused of a murder so devious, it fooled police for years. This morning, the prosecution will keep laying out its case against the cleveland woman accused of slowly poisoning her fiance, by spiking his favorite raspberry iced tea with antifreeze. In the summer of 2006, when the couple lived in this unassuming home with their children, a navy veteran and a father got violently ill. A few days later, the 31-year-old died. Back then, the coroner ruled he died of chronic intoxication by ethylene glyl. Four years later, police got a tip. And the nucorer ew coroner changed that cause to homicide. She was charged for aggravated murder and contaminating a substance for human consumption. On wednesday, friends took the stand, portraying him as a fun-loving guy that rarely drank. And they painted the couple's relationship as volatile. Two friends testified they had become so concerned, they adviedadvi advised him to change the beneficiary of his life insurance from his girlfriend to the father. He refused to do so. And on his death, she collected his life insurance policy and HIS 401(k), WITHOUT PAYING FOR Any of the funeral costs. Earlier in the week, the jury heard tearful testimony from his dearest friends. What did you do after learning of his death? I was distraught. What was your reaction? I almost fell down. I was in complete shock. Reporter: And she says she's not guilty. But now, it's up to a jury to decide if she's an innocent mom or a murderer who killed one sip at a time. Elizabeth? Gio, thanks so much. Let's bring in abc news chief legal affairs dan abrams for more on this case. This is the battle of two coroners. The defense maintains the victim killed himself. But would have to have drunk the antifreeze all at once. If this was done over a long period of time, that's a problem for the defendant. And that's the prosecution's theory here. The coroner saying, that this was chronic ingestion of the poison. Over months. A little bit at a time. Who would kill themselves doing a little bit at a time? The defense is going to call its own coroner to say, no, no. I think actually this occurred much more quickly. All at one time, in fact. That would support the defense's theory. How do you prove the differences? It's the one the jurors believe. That's why some of the other witnesses you just heard about become so important, which is the sort of why she would have done this. The human side behind this. And those are really crucial. But in the end, this case is going to come down to, do they believe the coroner? It takes them a while to file these charges. Five years before they went to trial. Does that mean the prosecution's case has problems or holes? It means they dn't feel they had a case back then. And they actually changed the cause of death. So, the coroner basically saying that initially I was uncertain. Then, he gets calls from friends and family members of his saying, you to look into this. We think we know exactly what happened here. And so, he looks into it. Then, this theory develops that this was this chronic poisoning. And the defense puts the victim on the stand in an essence, saying he had gambling debts, he felt decidual. We don't know they'll take the stand. We do know they're going to put him on trial. They're going to say he had real problems, there were real issues, and that's whey he wanted to commit suicide. We'll have more on the story as it develops, dan. Thank you very much.

This transcript has been automatically generated and may not be 100% accurate.

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